/Engine/Source/Runtime/MeshDescription/Public/MeshDescription.h
Determine whether a given edge is an internal edge between triangles of a specific polygon
bool IsEdgeInternalToPolygon ( const [FEdgeID](API\Runtime\MeshDescription\FEdgeID) EdgeID, const [FPolygonID](API\Runtime\MeshDescription\FPolygonID) PolygonID ) const